Interferon-?? (IFN-?) is known for its ability to restrict ongoing HIV replication, but with the advent of ART, interest in IFN-?'s activity against HIV waned. Exciting new data from a recent trial renews our interest as it suggests IFN-? may have activity against HIV reservoirs since integrated HIV DNA (but not total HIV DNA) was reduced in a subset of patients treated with IFN-? (pegylated interferon-?2A). This R21 proposal addresses a role for CTL as driving the decrease in HIV integration found with IFN-? therapy. Our rationale that IFN-? may enhance immune clearance is derived from the fact that HIV proteins can be expressed more efficiently from integrated HIV DNA than from unintegrated HIV DNA, which would lead to preferential clearance of integrated over unintegrated HIV DNA-the results found in vivo in the prior IFN-a trial. These findings led us to our overarching hypothesis: that IFN-? enhances immune clearance of the reservoir. We will use our latent model to further explore if IFN-? increases immune clearance by either making the reservoir more visible or by enhancing effector function. Our general approach is to purify CD4s and CD8s from ART infected patients and to treat these cells individually with IFN-? before coculture and then assess if reservoirs are reduced. We will compare these results to HDACi which are known to enhance HIV expression and are currently being tested for activity against HIV reservoirs in clinical trials. The effects of HDACi on antigen presentation and HIV specific CTL are unknown. We will dissect if the effects are on CD4s or CD8s and if HIV antigen expression, presentation or CTL function are enhanced by IFN-a. We will also compare and contrast IFN-? Responders and Nonresponders in the original trial to elucidate the essential steps to reservoir reduction. We are in a unique position to contribute to this question because of our expertise in measuring integrated HIV DNA and our ability to detect small changes in integration levels. We envision our study will lead to future better trial design and new insights that will be required for HIV eradication. Our specific aims are: Aim 1: Determine if IFN-? enhances clearance of latent cells in vitro and ex vivo by increasing HIV expression, antigen presentation, and/or CTL effectiveness and compare to the effects of HDACi to understand how IFN-? might reduce reservoirs. Aim 2: Examine if in vivo evidence in the prior IFN-a trial supports our model of CTL- mediated clearance.